cgroupfs: do not return errors from strconv.ParseInt() to write()

Arbitrary errors are not convertible to errnos for syscall return and cause the
sentry to panic.

PiperOrigin-RevId: 564782206

pkg/sentry/fsimpl/cgroupfs/devices.go

@@ -366,7 +366,7 @@ func toDeviceNumber(s string) (int64, error) {
 	}
 	val, err := strconv.ParseInt(s, 10, 64)
 	if err != nil {
-		return 0, err
+		return 0, linuxerr.EINVAL
 	}
 	return val, nil
 }